Adding two helper functions and modify upgrade to

work properly under MSSQL and Oracle. MDL-8303

lib/dmllib.php

@@ -1621,6 +1621,22 @@ function sql_as() {
     }
 }
 
+/**
+ * Returns the empty string char used by every supported DB. To be used when
+ * we are searching for that values in our queries. Only Oracle uses this
+ * for now (will be out, once we migrate to proper NULLs if that days arrives)
+ */
+function sql_empty() {
+    global $CFG;
+
+    switch ($CFG->dbtype) {
+        case 'oci8po':
+            return ' '; //Only Oracle uses 1 white-space
+        default:
+            return '';
+    }
+}
+
 /**
  * Returns the proper substr() function for each DB
  * Relies on ADOdb $db->substr property
@@ -1632,6 +1648,19 @@ function sql_substr() {
     return $db->substr;
 }
 
+/**
+ * Returns the SQL text to be used to compare one TEXT (clob) column with
+ * one varchar column, because some RDBMS doesn't support such direct
+ * comparisons.
+ * @param string fieldname the name of the TEXT field we need to order by
+ * @param string number of chars to use for the ordering (defaults to 32)
+ * @return string the piece of SQL code to be used in your statement.
+ */
+function sql_compare_text($fieldname, $numchars=32) {
+    return sql_order_by_text($fieldname, $numchars);
+}
+
+
 /**
  * Returns the SQL text to be used to order by one TEXT (clob) column, because
  * some RDBMS doesn't support direct ordering of such fields.

question/type/numerical/db/upgrade.php

@@ -27,7 +27,7 @@ function xmldb_qtype_numerical_upgrade($oldversion=0) {
     // from the empty string to *, to be like short answer questions.
     if ($result && $oldversion < 2006032201) {
         $result = set_field_select('question_answers', 'answer', '*',
-                "answer = '' AND question IN (SELECT id FROM {$CFG->prefix}question WHERE qtype = '" . NUMERICAL . "')");
+            sql_compare_text('answer') . " = '" . sql_empty() . "' AND question IN (SELECT id FROM {$CFG->prefix}question WHERE qtype = '" . NUMERICAL . "')");
     }
 
     return $result;